1. Field of the Invention
The present invention relates to a tool for forming a hem that may be used to secure two sheet metal panels together.
2. Background Art
Vehicle body panels such as deck lids, hoods, doors, and the like frequently include inner and outer panels that are secured together by means of a hem flange that extends about their periphery. Such body panels have traditionally been manufactured from steel sheet metal panels. Steel is very ductile and is easily formed in a hem forming operation. However, automotive manufacturers are increasingly turning to aluminum to obtain weight savings for vehicle body panels.
Aluminum alloys offer a high strength/low weight alternative to steel. Aluminum does not, however, have the same level of ductility. Forming a hem on a body panel made of aluminum sheet metal is more difficult than forming the same hem with steel sheet metal due to aluminum's reduced ductility compared to steel. An early solution to this problem was to form larger radius hems when working with aluminum sheet metal. Larger radius hems result in lower fit and finish ratings because larger radius hems make gaps appear larger between door closure panels and their openings. Further, the tendency of aluminum to tear or split at the radius of the hem caused by work hardening results in high part rejection rates and unacceptable scrap rates.
These and other problems relating to forming a hem flange and hem with aluminum sheet metal panels are addressed by applicants' invention.